Hybrid drive circuit for variable speed induction motor system and methods of control

ABSTRACT

Controllers for controlling hybrid motor drive circuits configured to drive a motor are provided herein. A controller is configured to drive the motor using an inverter when a motor commanded frequency is not within a predetermined range of line input power frequencies, and couple line input power to an output of the inverter using a first switch device when the motor commanded frequency is within the predetermined range of line input power frequencies.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.17/156,013, filed Jan. 22, 2021, further is continuation-in-part of U.S.patent application Ser. No. 16/126,530, filed Sep. 10, 2018 and adivision of U.S. patent application Ser. No. 14/854,766, filed Sep. 15,2015, whereas the entire contents and disclosure of which are herebyincorporated by reference herein.

BACKGROUND OF THE DISCLOSURE

The field of the invention relates generally to electric motors, and,more specifically to, hybrid motor drive circuits for induction motorsand methods of control.

At least some known permanent split capacitor (“PSC”) motors are fixedspeed motors that are most efficient when operating at line frequency.Such PSC motors have uncontrolled acceleration during startup. Further,at low load conditions, such PSC motors operate at a higher power levelthan necessary. Alternatively, variable speed motor controllers existthat adapt motor speed to the load level, but are limited by powerfactor, electromagnetic interference, and electronic lossconsiderations.

BRIEF DESCRIPTION OF THE DISCLOSURE

In one aspect, a controller for controlling a motor is provided. Thecontroller is configured to drive the motor using an inverter when amotor commanded frequency is not within a predetermined range of lineinput power frequencies, and couple line input power to an output of theinverter using a first switch device when the motor commanded frequencyis within the predetermined range of line input power frequencies.

In another aspect, a controller for controlling a motor is provided. Thecontroller is configured to operate a switch device configured to bypassa run capacitor of the motor when a motor commanded frequency is notwithin a predetermined range of line input power frequencies; andsynchronize two phases of a inverter to apply an output voltage to themotor that is substantially equivalent to line input voltage when themotor commanded frequency is within the predetermined range of lineinput power frequencies.

In yet another aspect, a controller for controlling a motor is provided.The controller is configured to realize, using a bi-directional powerconverter, bidirectional power transfer of AC line input power receivedfrom a power source and regenerated power from the motor; synchronizemultiple outputs of the inverter by providing two inverter phases withthe same command; and enable regeneration of power from the motor to thepower source when instantaneous power of the motor becomes negative.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a hybrid motor system.

FIG. 2 is a circuit diagram of a hybrid motor system.

FIG. 3A is a block diagram of a hybrid motor system.

FIG. 3B is a block diagram of the hybrid motor system shown in FIG. 3Ain a drive mode.

FIG. 3C is a block diagram of the hybrid motor system shown in FIG. 3Ain a PSC mode.

FIG. 4 is a circuit diagram of a hybrid motor system.

FIG. 5 is a circuit diagram of a hybrid twin motor system.

DETAILED DESCRIPTION OF THE DISCLOSURE

FIG. 1 is a block diagram of a hybrid motor system 100. In the exemplaryembodiment, hybrid motor system 100 includes a motor 102 and a drivecircuit 104 coupled to and configured to control operation of motor 102.In the exemplary embodiment, motor 102 is a permanent split capacitor(PSC) motor that includes a main winding 106, a start winding 108, and acapacitor 110. Drive circuit 104 includes a rectifier 112 configured toreceive alternating current (AC) line power input to first and secondinput terminals 114 and 116 from a power source 118, an inverter 120coupled downstream from rectifier 112, a direct current (DC) link 122defined between rectifier 112 and inverter 120, a DC link capacitor 124coupled across DC link 122, a main switch device 126 configured toselectively couple the AC line power to an output of inverter 120, abypass switch device 128 configured to selectively bypass capacitor 110,and a controller 130 configured to control operation of drive circuit104 to drive motor 102.

In the exemplary embodiment, drive circuit 104 receives the AC lineinput power at first and second input terminals 114 and 116 from an ACpower source, such as a utility. Rectifier 112 is configured to rectifythe AC line power received at first and second input terminals 114 and116 to pulsed DC power. DC link capacitor 124 stores the pulsed DC poweron DC link 122 and provides a DC link voltage to inverter 120. In theexemplary embodiment, DC link capacitor 124 has a capacitance up toabout 1,000 microfarads (μF) to substantially maintain the voltage onthe DC link to a DC value.

Inverter 120 is a 3-phase inverter and includes first switches 132associated with a first phase, second switches 134 associated with asecond phase, and third switches 136 associated with a third phase of3-phase inverter 120. In the exemplary embodiment, main winding 106 ofmotor 102 is coupled to a common node 138 between first switches 132 andto a common node 140 between second switches 134. Moreover, in theexemplary embodiment, start winding 108 of motor 102 is coupled tocommon node 140 between second switches 134 and to a common node 142between third switches 136. Capacitor 110 is coupled between startwinding 108 and common node 142 between third switches 136. Based onsignals received from controller 130, inverter 120 is configured toconvert the DC link voltage to a two-phase AC output voltage for drivingmotor 102 to optimize machine efficiency.

First switch device 126 is coupled to first and second input terminals114 and 116 and is coupled in parallel to the output of inverter 120. Inthe exemplary embodiment, first switch device 126 is operated bycontroller 130 to selectively couple the AC line power to the output ofinverter 120 such that the AC line power may be applied directly to mainwinding 106 and start winding 108. Controller 130 determines whether toopen or close first switch device 126 based on an operational frequencyof motor 102 or a commanded motor reference point (e.g., a speedsetting).

Bypass switch device 128 is coupled in parallel with capacitor 110 ofmotor 102. More specifically, bypass switch device 128 is coupledbetween a pole of start winding 108 and common node 138 between thirdswitches 136. However, capacitor position can be reversed as long as thecapacitor is in series with the start winding. Bypass switch device 128is operated by controller 130 to selectively bypass capacitor 110 whenmotor 102 is operating with the inverter at a frequency different than afrequency band around the line power frequency of power source 118. Morespecifically, capacitor 110 is provided in motor 102 to generate a phaseshift required to start motor 102 in a standard across the line PSC. Inthe hybrid drive, the starting of the motor can be done through theinventor with the capacitor 110 bypassed.

In the exemplary embodiment, controller 130 includes a processor 144 anda memory device 146. In the exemplary embodiment, controller 130 isimplemented in one or more processing devices, such as amicrocontroller, a microprocessor, a programmable gate array, a reducedinstruction set circuit (RISC), an application specific integratedcircuit (ASIC), etc. Accordingly, in this exemplary embodiment,controller 130 is constructed of software and/or firmware embedded inone or more processing devices. In this manner, controller 130 isprogrammable, such that instructions, intervals, thresholds, and/orranges, etc. may be programmed for a particular motor 102 and/or anoperator of motor 102. Controller 130 may be wholly or partiallyprovided by discrete components, external to one or more processingdevices.

In operation, controller 130 is configured to receive a frequencycommanded for motor 102 and compare it to a predetermined range of lineinput power frequencies. Controller 130 is configured to activate orclose first switch device 126 when the frequency commanded by motor 102is within the predefined range of line input power frequencies. Closingfirst switch device 126 couples first and second input terminals 114 and116 to the output of inverter 120 such that the line input power isapplied directly to main winding 106 and start winding 108 and capacitor110 of motor 102. As used herein, a “PSC mode” of operation is when lineinput power is applied directly to motor 102. When operating in PSCmode, motor 102 is operated at a fixed speed based on the line inputpower.

Additionally, or alternatively, controller 130 is configured to openfirst switch device 126 when the frequency commanded by motor 102 is notwithin the predefined range of line input power frequencies. Openingfirst switch device 126 causes inverter 120 to provide conditioned powerto motor 102. As used herein, a “drive mode” of operation is wheninverter 120 provides conditioned power to motor 102. When operating indrive mode, controller 130 uses pulse width modulation (PWM) to controlswitches of inverter 120, which enables variable speed control of motor102.

Hybrid motor system 100 combines the low-speed operating points, softstarting, and controlled acceleration benefits of a variable speed drivecircuit with the line operable, increased power factor, and reducedelectromagnetic interference (EMI) signature benefits of a fixed speedPSC motor to improve overall system operation. More specifically, ratherthan drive motor 102 at a nominal 60 Hz regardless load demand, hybridPSC motor system 100 adjusts to lighter loads by reducing the speed ofmotor 102. Drive circuit 104 is provided to control motor 102 atvariable speeds to adapt to changing loads, especially in lower inputpower ranges where fixed-speed PSC motors are typically less efficient.Further, at higher input power ranges, the drive mode of drive circuit104 may have a reduced power factor, increased EMI signatures, and/orelectronic losses. When the frequency commanded by motor 102 is withinthe predefined range of line input power frequencies, hybrid motorsystem 100 switches from drive mode to PSC mode. By switching betweendrive mode and PSC mode, hybrid PSC motor system 100 provides technicaleffects including high PF, low EMI, high efficiency, variable speedoperation, and control of the starting acceleration. Further, becausedrive circuit 104 does not have to operate at full power because, atfull power, the AC line power is coupled to the output of inverter 120,the size of drive circuit may be reduced.

By using inverter 120 to drive motor 102 in drive mode when the motorcommanded frequency is not within the predetermined range of line inputpower frequencies, drive circuit 104 reduces inrush current, enablessoft starting of motor 102, and enables controlled acceleration of motor102 during startup. More specifically, controller 130 modulates a dutycycle of the switches of inverter 120 to produce motor currents tomaximize torque produced by motor 102 during startup. Further,controller 130 is configured to adjust stator frequency of motor 102 tominimize torque pulsation and apply a predetermined acceleration ramprate. Alternatively, controller 130 is configured to adjust statorfrequency by monitoring motor current and adjusting a ramp rate toremain below a predetermined limit.

In one embodiment, hybrid motor system 100 reduces motor capacitorinrush current in bypass switch device 128. Specifically, to reducemotor capacitor inrush current, controller 130 controls timing of bypassswitch device 128. More specifically, controller 130 monitors AC linevoltage, DC-link voltage, and/or AC line current. Controller 130operates bypass switch device 128 when the AC line voltage and/or the ACline current are at a minimal value, which limits inrush current inbypass switch device 128. In another embodiment, the voltage and/orcurrent in the bypass switch are monitored and estimated and thecontroller operates the opening of the bypass switch when the current isminimal to minimize the effect of transient voltage and current duringopening that may be damaging to the bypass switch.

In one embodiment, hybrid motor system 100 reduces transient voltagesand currents in switch device 126. To reduce transient voltages andcurrents in switch device 126, controller 130 monitors AC line voltage,DC-link voltage, and/or AC line current. Controller 130 operates switchdevice 126 when the AC line voltage and/or the AC line current are at aminimal value, which limits inrush current in switch device 126. In someembodiments, controller 130 is configured to monitor motor phasecurrents to minimize the torque drop when changing mode of operation. Insome embodiments, controller 130 is configured to estimate or measuremotor terminal voltages to minimize phase difference with AC linevoltage and minimize torque pulsation at transition.

In another embodiment, hybrid motor system 100 monitors for a lockedrotor condition during both starting and normal operation. Controller130 compares applied motor voltages and measured motor currents tothreshold values. Controller 130 may determine that there is a lockedrotor condition when the applied motor voltages and measured motorcurrents exceed the threshold values.

In some embodiments, hybrid motor system 100 is configured to monitor ACpower factor to provide de-rated operation, if necessary. When operatingmotor 102 using inverter 120, controller 130 is configured to receivemotor speed and torque information for motor 102. Based on the motorspeed and torque information, controller 130 computes an input power orcurrent limit that drive circuit 104 may draw from power source 118 toavoid exceeding the power ratings of drive circuit 104.

In an alternative embodiment, controller 130 measures a value of AC linecurrent and compares the value of AC line current to a predefined valueof AC line current. If the measured AC line current exceeds thepredefined value of AC line current, controller 130 provides de-ratedoperation of system 100 to stay within the limits of the line/breakercapacity.

In some embodiments, hybrid PSC motor system 100 is configured toimplement transient motor acceleration and synchronization to reducetransients when switching between modes of operation. In one embodiment,controller 130 is configured to monitor motor phase currents to minimizethe torque drop when changing mode of operation. In another embodiment,controller 130 is configured to estimate or measure motor terminalvoltages to minimize a phase difference with AC line voltage andminimize torque pulsation at the transition.

FIG. 2 is a block diagram of a hybrid motor system 200. Components ofhybrid motor system 200 similar to those described in hybrid motorsystem 100 (shown in FIG. 1 ) are referenced in FIG. 2 using the samereference labels used in FIG. 1 and their descriptions are not berepeated herein.

In the exemplary embodiment, hybrid motor system 200 operates in thesame manner as hybrid motor system 100, except system 200 does notinclude bypass switch device 128. Rather, hybrid motor system 200includes main winding 106 coupled to the first phase output of inverter120. Moreover, in the exemplary embodiment, start winding 108 includesan input coupled to the second phase output of inverter 120 and anoutput coupled to a third phase output of inverter 120. Capacitor 110includes an input coupled to the third phase output of inverter 120 andan output. The positioning of capacitor 110 in hybrid motor system 200enables operation without bypass switch device 128.

FIG. 3A is a block diagram of a hybrid motor system 300. FIG. 3B is ablock diagram of hybrid motor system 300 in drive mode. FIG. 3C is ablock diagram of hybrid motor system 300 in PSC mode. Components ofhybrid PSC motor system 300 similar to those described in hybrid motorsystem 100 (shown in FIG. 1 ) are referenced in FIGS. 3A, 3B, and 3Cusing the same reference labels used in FIG. 1 and their descriptionsare not be repeated herein. System 300 differs from system 100 byremoving first switching device 126 and using a greatly reduced DC-linkcapacitance than system 100.

In the exemplary embodiment, hybrid motor system 300 includes motor 102and drive circuit 104 coupled to and configured to control operation ofmotor 102. In the exemplary embodiment, motor 102 is a permanent splitcapacitor (PSC) motor. In the exemplary embodiment, DC link capacitor124 has a capacitance between about 0.1 μF and about 10 μF.

In the exemplary embodiment, drive circuit 104 receives the AC lineinput power at first and second input terminals 114 and 116 from an ACpower source, such as a utility. Rectifier 112 is configured to rectifythe AC line power received at first and second input terminals 114 and116 to pulsed DC power. DC link capacitor 124 stores a small amount ofDC power on DC link 122 and provides a DC link voltage to inverter 120.

In operation, controller 130 is configured to receive a frequencycommanded for motor 102 and compare it to a predetermined range of lineinput power frequencies.

When the frequency commanded for motor 102 is not within thepredetermined range of line input power frequencies, drive circuit 104operates in drive mode to apply variable speed control to operate motor102, as shown in FIG. 3B. More specifically, in the exemplaryembodiment, drive circuit 104 has a low DC link capacitance (i.e., lessthan 100 μF) and uses a bypass switch device 328 to bypass capacitor110. Controller 130 closes bypass switch device 328 to electricallyshort capacitor 110 and controls 2-phase switching of inverter 120 toachieve the variable speed control.

Because only low capacitance capacitor 124 is used in motor drivecircuit 300, large amounts of voltage are not stored on DC link 122 ofmotor drive circuit 300. Rather, in the exemplary embodiment, drivecircuit 300 stores energy on a rotational load, which is coupled to arotatable shaft (not shown) of motor 102. More specifically, in theexemplary embodiment, the load is a mechanical energy storage device(i.e., a compressor, a condenser fan, or a blower). For example, m oneembodiment, the load may be a compressor, a condenser fan, or a blowerin an HVAC system.

During operation, in the exemplary embodiment, rectifier 112 rectifiesthe AC line input voltage received from power source 118 into a pulsedAC. When AC line input voltage is available, controller 130 isconfigured to increase energy transfer from motor 102 to be stored onthe load as inertia. More specifically, when input voltage is available,the torque increases, causing the rotational speed of the load to alsoincrease. In the exemplary embodiment, the inertia of the load limitsspeed variations of the motor 102, which enables torque production tocontinue when input voltage is unavailable.

In one embodiment, while input voltage is available, controller 130 alsocauses small amounts of voltage to be stored on DC-link capacitor 124.When the AC line input voltage approaches zero, capacitor 124 providesthe stored voltage to motor 102.

As the input voltage begins to drop, torque produced on the load bymotor 102 turns into rotational speed. As AC line input voltageapproaches zero or DC link voltage has approximately 100% voltageripple, controller 130 mitigates a reduction in energy transfer from theload to motor 102 to produce positive torque. More specifically,controller 130 controls current flowing to motor 102 such that motor 102continues producing torque when input voltage to motor 102 approacheszero or equals zero. In an alternative embodiment, controller 130 alsomanages energy transfer from capacitor 124 to motor 102. These energytransfers enable motor 102 to operate while input voltage is low orunavailable during each phase of the pulsed DC voltage.

As shown in FIG. 3C, when the frequency commanded by motor 102 is withinthe predetermined range of line input power frequencies, controller 130is configured to synchronize an output of motor drive circuit 104 tooperate motor 102 at a full load with a frequency that is about twotimes greater than a line input frequency. Specifically, controller 130synchronizes the first and third phases of inverter 120 to apply anoutput voltage that is substantially equivalent to line input voltage.

Hybrid motor system 300 achieves similar benefits to hybrid PSC motorsystem 100 without using switching device 126 (shown in FIG. 1 ) tocouple the AC line power to an output of inverter 120. Rather, hybridmotor system 300 uses a small DC link capacitance with switching device136 to bypass capacitor 110 in drive mode when the frequency commandedby motor 102 is not within the predefined range of line input powerfrequencies. When the frequency commanded by motor 102 is within thepredefined range of line input power frequencies, hybrid motor system300 implements a control method to synchronize electronic drive outputto operate at twice the frequency of the utility using a PSC motordesigned for a full load. Hybrid motor system 300 provides technicaleffects including high PF, low EMI, high efficiency, variable speedoperation, and control of the starting acceleration. Further, becausedrive circuit 104 does not have to operate at full power because, atfull power, the AC line power is coupled to the output of inverter 120,the size of drive circuit may be reduced.

In one embodiment, hybrid motor system 300 controls drive circuit 104output state to limit power regeneration on DC-link capacitor 124. Drivecircuit 104 uses low-capacitance DC-link capacitor 124 to maximize aconduction interval of the power converter and maximize power factor.Controller 130 measures the DC-link voltage, current of inverter 120, oran instantaneous power of motor 102. Controller 130 modifies a voltagecommanded to inverter 120 to minimize a flow of current from motor 102to DC-link capacitor 124.

In one embodiment, hybrid motor system 300 controls drive circuit 104output state to synchronize multiple outputs of inverter 120 byproviding two inverter phases with the same command. Controller 130 thenswitches inverter phases to apply either a positive voltage or negativevoltage to motor 102, depending on a polarity of the line input voltage.Controller 130 commutates inverter 120 at low frequency within afrequency band of about twice the frequency of power source 118.

By using inverter 120 to drive motor 102 in drive mode when the motorcommanded frequency is not within the predetermined range of line inputpower frequencies, drive circuit 104 reduces inrush current, enablessoft starting of motor 102, and enables controlled acceleration of motor102 during startup. More specifically, controller 130 modulates a dutycycle of the switches of inverter 120 to produce motor currents tomaximize torque produced by motor 102 during startup. Further,controller 130 is configured to adjust stator frequency of motor 102 tominimize torque pulsation and apply a predetermined acceleration ramprate. Alternatively, controller 130 is configured to adjust statorfrequency by monitoring motor current and adjusting a ramp rate toremain below a predetermined limit.

In one embodiment, hybrid motor system 300 reduces motor capacitor 110inrush current in bypass switch device 328. Specifically, to reducemotor capacitor 110 inrush current, controller 130 controls timing ofbypass switch device 328. More specifically, controller 130 monitors ACline voltage, DC-link voltage, and/or AC line current. Controller 130operates bypass switch device 328 when the AC line voltage and/or the ACline current are at a minimal value, which limits inrush current inbypass switch device 328.

In another embodiment, hybrid motor system 300 monitors for a lockedrotor condition during both starting and normal operation. Controller130 compares applied motor voltages and measured motor currents tothreshold values. Controller 130 may determine that there is a lockedrotor condition when the applied motor voltages and measured motorcurrents exceed the threshold values.

In some embodiments, hybrid motor system 300 is configured to monitor ACpower factor to provide de-rated operation, if necessary. When operatingmotor 102 using inverter 120, controller 130 is configured to receivemotor speed and torque information for motor 102. Based on the motorspeed and torque information, controller 130 computes an input power orcurrent limit that drive circuit 104 may draw from power source 118 toavoid exceeding the power ratings of drive circuit 104.

In an alternative embodiment, controller 130 measures a value of AC linecurrent and compares the value of AC line current to a predefined valueof AC line current. If the measured AC line current exceeds thepredefined value of AC line current, controller 130 provides de-ratedoperation of system 100 to stay within the limits of the line/breakercapacity.

In some embodiments, hybrid motor system 300 is configured to implementtransient motor acceleration and synchronization to reduce transientswhen switching between modes of operation. In one embodiment, controller130 is configured to monitor motor phase currents to minimize the torquedrop when changing mode of operation. In another embodiment, controller130 is configured to estimate or measure motor terminal voltages tominimize a phase difference with AC line voltage and minimize torquepulsation at the transition.

FIG. 4 is a block diagram of a hybrid motor system 400. Components ofhybrid motor system 400 similar to those described in PSC motor system100 (shown in FIG. 1 ) are referenced in FIG. 4 using the same referencelabels used in FIG. 1 and their descriptions are not be repeated herein.System 400 differs from system 100 by removing first switching device126, using a much lower DC link capacitance as compared to system 100,and using a bi-directional front-end power converter to realizebi-directional power transfer between a utility and motor 102.

In the exemplary embodiment, hybrid motor system 400 includes motor 102and drive circuit 104 coupled to and configured to control operation ofmotor 102. Motor 102 includes main winding 106, start winding 108, andcapacitor 110. In the exemplary embodiment, motor 102 is a permanentsplit capacitor (PSC) motor. Drive circuit 104 includes a bi-directionalfront-end power converter 412 configured to receive AC line power inputto first and second input terminals 114 and 116 from power source 118,inverter 120 coupled downstream from rectifier 112, a DC link 122defined between bi-directional front-end power converter 412 andinverter 120, and DC link capacitor 124 coupled across DC link 122. Inthe exemplary embodiment, DC link capacitor 124 has a capacitancebetween about 0.1 μF and about 10 μF.

In the exemplary embodiment, drive circuit 104 receives the AC lineinput power at first and second input terminals 114 and 116 from an ACpower source, such as a utility. Bi-directional front-end powerconverter 412 is configured to convert the AC line power received atfirst and second input terminals 114 and 116 to pulsed DC power.Additionally, when power is regenerated from motor 102, bi-directionalfront-end power converter 412 is configured to provide the regeneratedpower back to power source 118.

Inverter 120 is a 3-phase inverter and includes first switches 132associated with a first phase, second switches 134 associated with asecond phase, and third switches 136 associated with a third phase of3-phase inverter 120. In the exemplary embodiment, main winding 106 ofmotor 102 is coupled to a common node 138 between first switches 132 andto a common node 140 between second switches 134. Moreover, in theexemplary embodiment, start winding 108 of motor 102 is coupled tocommon node 140 between second switches 134 and to a common node 142between third switches 136. Capacitor 110 is coupled between startwinding 108 and common node 142 between third switches 136. Based onsignals received from controller 130, inverter 120 is configured toconvert the DC link voltage to a single-phase AC output voltage fordriving motor 102.

Bypass switch device 128 is coupled in parallel with capacitor 110 ofmotor 102. More specifically, bypass switch device 128 is coupledbetween a side of start winding 108 and common node 138 between thirdswitches 136. Bypass switch device 128 is operated by controller 130 toselectively bypass capacitor 110 when motor 102 is not operating at aline power frequency of power source 118.

In one embodiment, hybrid motor system 400 controls drive circuit 104output state to limit power regeneration on DC-link capacitor 124. Drivecircuit 104 uses low-capacitance DC-link capacitor 124 to maximize aconduction interval of the power converter and maximize power factor.Controller 130 measures the DC-link voltage, current of inverter 120, oran instantaneous power of motor 102. Controller 130 modifies a voltagecommanded to inverter 120 to minimize a flow of current from motor 102to DC-link capacitor 124.

In one embodiment, hybrid motor system 400 controls drive circuit 104output state to synchronize multiple outputs of inverter 120 byproviding two inverter phases with the same command. Controller 130 thenswitches inverter phases to apply either a positive voltage or negativevoltage to motor 102, depending on a polarity of the line input voltage.Controller 130 commutates inverter 120 at low frequency within afrequency band of about twice the frequency of power source 118.

In one embodiment, hybrid motor system 400 controls bi-directionalfront-end power converter 412 to enable regeneration when instantaneouspower of motor 102 becomes negative. Controller 130 is configured tomeasure the DC-link voltage and determine whether the DC-link voltage ishigher than AC line voltage. Alternatively, controller 130 may measureinstantaneous power of motor 102 or current of inverter 120. Controller130 then assesses whether instantaneous power is negative. If theinstantaneous power is negative, controller 130 commands bi-directionalfront-end power converter 412 to couple drive circuit 104 across theline input power to enable the current to flow back to power source 118.

By using inverter 120 to drive motor 102 in drive mode when the motorcommanded frequency is not within the predetermined range of line inputpower frequencies, drive circuit 104 reduces inrush current, enablessoft starting of motor 102, and enables controlled acceleration of motor102 during startup. More specifically, controller 130 modulates a dutycycle of the switches of inverter 120 to produce motor currents tomaximize torque produced by motor 102 during startup. Further,controller 130 is configured to adjust stator frequency of motor 102 tominimize torque pulsation and apply a predetermined acceleration ramprate. Alternatively, controller 130 is configured to adjust statorfrequency by monitoring motor current and adjusting a ramp rate toremain below a predetermined limit.

In one embodiment, hybrid motor system 400 reduces motor capacitor 110inrush current in bypass switch device 128. Specifically, to reducemotor capacitor 110 inrush current, controller 130 controls timing ofbypass switch device 128. More specifically, controller 130 monitors ACline voltage, DC-link voltage, and/or AC line current. Controller 130operates bypass switch device 128 when the AC line voltage and/or the ACline current are at a minimal value, which limits inrush current inbypass switch device 128. In another embodiment, the voltage and/orcurrent in the bypass switch are monitored or estimated and thecontroller operates the opening of the bypass switch when the current isminimal to minimize the effect of transient voltage and current duringopening that may be damaging to the bypass switch.

In another embodiment, hybrid motor system 400 monitors for a lockedrotor condition during both starting and normal operation. Controller130 compares applied motor voltages and measured motor currents tothreshold values. Controller 130 may determine that there is a lockedrotor condition when the applied motor voltages and measured motorcurrents exceed the threshold values.

In some embodiments, hybrid motor system 400 is configured to monitor ACpower factor to provide de-rated operation, if necessary. When operatingmotor 102 using inverter 120, controller 130 is configured to receivemotor speed and torque information for motor 102. Based on the motorspeed and torque information, controller 130 computes an input power orcurrent limit that drive circuit 104 may draw from power source 118 toavoid exceeding the power ratings of drive circuit 104.

In an alternative embodiment, controller 130 measures a value of AC linecurrent and compares the value of AC line current to a predefined valueof AC line current. If the measured AC line current exceeds thepredefined value of AC line current, controller 130 provides de-ratedoperation of system 100 to stay within the limits of the line/breakercapacity.

In some embodiments, hybrid motor system 400 is configured to implementtransient motor acceleration and synchronization to reduce transientswhen switching between modes of operation. In one embodiment, controller130 is configured to monitor motor phase currents to minimize the torquedrop when changing mode of operation. In another embodiment, controller130 is configured to estimate or measure motor terminal voltages tominimize a phase difference with AC line voltage and minimize torquepulsation at the transition.

FIG. 5 is a circuit diagram of an exemplary hybrid twin motor system 500that may use any of hybrid motor systems 100, 200, 300, 400 (shown inFIGS. 1-4 ). In the exemplary embodiment, hybrid twin motor system 400includes a common motor drive circuit 502 that combines commoncomponents of a compressor motor drive circuit and a condenser motordrive circuit. More specifically, in the exemplary embodiment, hybridtwin motor system 500 includes common motor drive circuit 502, a firstelectric motor 504 having a first motor drive circuit 506, a secondelectric motor 508 having a second motor drive circuit 510 and a motorcontroller 512. System 500 is referred to as a hybrid system because itmay use either a low-capacitance capacitor (between about 0.1 μF andabout 100 μF) or a large DC capacitor (over 1000 μF) in first motordrive circuit 506 and a high-capacitance capacitor (between about 200 μFand 1000 μF) in second motor drive circuit 510.

In the exemplary embodiment, and as described herein, first electricmotor 504 is a compressor motor 504 for a compressor 514, first motordrive circuit 506 is a compressor motor drive circuit 506, secondelectric motor 508 is a condenser fan motor 508 for a condenser fan 516,and second motor drive circuit 510 is a condenser fan motor drivecircuit 510. In the exemplary embodiment, compressor motor drive circuit506 is loaded by compressor motor 504, which has a power capabilitybetween about 1.5 HP-7.5 HP, and condenser fan motor drive circuit 510is loaded by a condenser fan motor 508, which has a power capability ofabout ⅓ HP.

In the exemplary embodiment, common motor drive circuit 502 includes asurge protection device 518 configured to be coupled to a power supply520, an electromagnetic interference (EMI) filter 522, a rectifier 524,a first DC-link 526 defined by a positive DC-link rail 528 and anegative DC-link rail 530, a low-capacitance capacitor 532 coupledacross first DC link 526, and a hall sensor 534 coupled to positiveDC-link rail 528.

Surge protection device 518 includes a line-to-line metal oxide varistor(MOV) 536, a line-to-ground MOV 538, and a gas discharge tube (GDT) 540.Surge protection device 518 is configured to provide lightningprotection for hybrid twin motor system 500 when there is a surge involtage from power supply 520. In the exemplary embodiment, power supply520 is a single phase alternating current power source, such as anelectrical grid or utility, that supplies a sine wave input voltage. EMIfilter 522 is configured to prevent EMI noise from coupling back topower supply 520. The signals output from EMI filter 522 are applied torectifier 524, which transforms the sine wave input voltage to arectified AC voltage.

Low-capacitance capacitor 532 is configured to store small amounts ofenergy when input voltage is available. In the exemplary embodiment,low-capacitance capacitor 532 is a film capacitor and has a capacitancebetween about 0.1 μF and about 100 μF. The use of bulky, unreliableelectrolytic filter capacitors in common motor drive circuit 502 isavoided. Low-capacitance capacitor 532 is used as the energy storagecomponent for compressor motor 504. Further, low-capacitance capacitor532 facilitates increasing a power factor of hybrid twin motor system500 to at least about 0.9.

Hall sensor 534 is coupled to positive DC-link rail 528 afterlow-capacitance capacitor 532 and is configured to provide ground faultprotection when large current flows through positive DC-link rail 528.In the exemplary embodiment, current is considered a large current whenit is larger than a normal operating current of the particular electricmotor and may be higher than 100 Amps in a typical 240 V AC-line system.In one embodiment, a ground fault occurs when current supplied from apower supply goes directly to earth ground and does not return to thenormal power lines due to damage of motor insulation, which createslarge, short circuit current and may damage semiconductor devices in thesystem. Hall sensor 534 senses current on positive DC-link rail 528 andoutputs a fault signal to motor controller 512 and receives a resetsignal from motor controller 512.

In the exemplary embodiment, compressor motor drive circuit 506 iscoupled to first DC-link 526 downstream from hall sensor 534. Compressormotor drive circuit 506 includes an inverter 536 configured to becoupled to compressor motor 504. In the exemplary embodiment, inverter536 is a three-phase DC-AC voltage source inverter. Inverter 536 isconfigured to receive control signals from motor controller 512 andsupply compressor motor 504 with conditioned AC voltage accordingly.

In the exemplary embodiment, inverter 536 is a three-phase inverter andincludes a set of inverter switches for each of the three phases.Inverter 536 also includes first, second, and third shunt resistors 538coupled to respective sets of inverter switches and to said negativeDC-link rail 530. In another embodiment, inverter 536 includes one shuntresistor 540 coupled to negative DC-link rail 530. In either case, shuntresistors 538 or shunt resistor 540 are configured to sense current onnegative DC-link rail 530 to provide ground fault current protection fornegative DC-link rail 530.

In the exemplary embodiment, motor controller 512 1s programmed tocontrol operation of both compressor motor 504 and condenser fan motor508 of hybrid twin motor system 500. More specifically, motor controller512 includes a first control unit 542 operable to perform currentcontrol and pulse-width modulated (PWM) signal generation for compressormotor 504 and a second control unit 544 operable to perform currentcontrol and pulse-width modulated signal generation for condenser fanmotor 508.

First control unit 542 is configured to implement DPT control of powersupplied to drive compressor 514. More specifically, first control unit542 is configured to increase energy transfer from compressor motor 504to compressor 514 when input voltage is available and to mitigate areduction in energy transfer from compressor 514 to compressor motor 504to produce positive torque when DC-link voltage has approximately 100%voltage ripple. To control compressor 514, first control unit 542 isconfigured to generate PWM signals that are applied to inverter 536 tocontrol rotation of compressor motor 504. Additionally, first controlunit 542 is configured to receive the fault signal from hall sensor 534and processed shunt currents from shunt resistors 538, and in responseto a ground fault, disables any PWM signals to inverter 536 to removepower to compressor motor 504 during a fault.

In the exemplary embodiment, second or condenser fan motor drive circuit510 includes a diode 546, a negative temperature coefficient (NTC)resistor 548, a second DC-link 550 defined by a second positive DC-linkrail 552 and a second negative DC-link rail 554, a high-capacitancecapacitor 556 coupled across second DC link 550, an inverter 558, andone or three shunt resistors 560 or 562.

Diode 546 and NTC resistor 548 are coupled between low-capacitancecapacitor 532 and high-capacitance capacitor 556. More specifically,diode 546 and NTC resistor 548 are coupled after hall sensor 534 so thathall sensor 534 may also provide ground fault protection for condenserfan motor 508. In the exemplary embodiment, diode 546 and NTC resistor548 are configured to provide inrush current protection for condenserfan motor drive circuit 510 that may be caused by the presence ofhigh-capacitance capacitor 556.

In the exemplary embodiment, high-capacitance capacitor 556 has acapacitance between about 200 μF and 1000 μF. High-capacitance capacitor556 receives the rectified AC voltage generated by rectifier 524 andgenerate a smoothed DC voltage which is applied to inverter 558.

Inverter 558 is configured to be coupled to condenser fan motor 508. Inthe exemplary embodiment, inverter 558 is a three-phase DC-AC voltagesource inverter. Inverter 558 is configured to receive control signalsfrom motor controller 512 and supply condenser fan motor 508 withconditioned AC voltage accordingly.

In the exemplary embodiment, inverter 558 is a three-phase inverter andincludes a set of inverter switches for each of the three phases.Inverter 558 also includes first, second, and third shunt resistors 562coupled to respective sets of inverter switches and to negative DC-linkrail 554. In another embodiment, inverter 558 includes one shuntresistor 564 coupled to negative DC-link rail 554. In either case, shuntresistors 562 or shunt resistor 564 are configured to sense current onnegative DC-link rail 554 to provide ground fault current protection fornegative DC-link rail 554.

In the exemplary embodiment, second control unit 544 1s configured togenerate PWM signals that are applied to inverter 558 to controlrotation of condenser fan motor 508 using energy stored onhigh-capacitance capacitor 556. Additionally, second control unit 544 isconfigured to receive the fault signal from hall sensor 534 andprocessed shunt currents from shunt resistors 562, and in response to aground fault, disables any PWM signals to inverter 558 to remove powerto condenser fan motor 508 during a fault.

In some embodiments, hybrid motor system 500 additionally includes oneor more blower motors and one or more associated blower motor drivecircuits. In such implementations, system 500 is a hybrid triple or“trio” motor system. Each of the one or more blower motor drive circuitsinclude similar components and operate similarly to condenser fan motordrive circuit 510. In such embodiments, a single drive circuit wouldcontrol operation of compressor 514, condenser fan 516, and the one ormore blowers.

In another embodiment, any of hybrid motor systems 100, 200, 300, 400may be used in an air conditioning system that includes a heat pumpadding heating capability to the typical cooling system, a reversingvalve that directs a flow of coolant between indoor and outdoor coils,and an expansion valve. In the exemplary embodiment, the PSC motor maybe one of hybrid motor systems 100, 200, 300, 400. When using the heatpump, a reversing valve is used for directional changes only. In bothheat pump and cooling modes, an expansion valve is used to relievepressure. Hybrid motor systems 100, 200, 300, 400 may be configured tocontrol the compressor PSC motor and integrate control of the reversingand/or expansion valve on a single board electronic control.

In addition to compressors, blowers, and fans, some implementations ofthe hybrid motor systems 100, 200, 300, 400 operate one or more pumpmotors. In some implementations, the hybrid motor system (e.g., hybridmotor system 100, 200, 300, or 400) operates the motor below linefrequency or above line frequency for overspeed, if needed. In someimplementations, hybrid motor systems 100, 200, 300, 400 are configuredto operate in a “limp” mode when a drive failure occurs. If the hybridmotor system 100, 200, 300, 400 detects a drive failure, the hybridmotor system defaults to line operation all the time. In someimplementations, the hybrid motor system selectively applies powerfactor correction (PFC) or active power factor correction (“APFC”)(i.e., only as needed) to meet agency or circuit rating requirementsregarding power factor. In some implementations the hybrid motor systemapplies an algorithm that optimizes the balance of currents between themotor windings. More specifically, the hybrid motor system measures themotor currents and adjusts the ratio of voltage command between windingsto minimize the root mean squared (“RMS”) current in the stator whilemaximizing the system output power (i.e., torque and speed, that areestimated or calculated). Accordingly, the algorithm characterizes themotor controlled by the hybrid motor system. In some implementations,the hybrid motor system performs rotation sensing. More specifically,the hybrid motor system operates the motor at a first speed in a firstdirection, then determines a first time required to accelerate to thefirst speed and/or the torque at the first speed, then operates themotor in a second direction that is the opposite of the first directionat the first speed and determines a second time required to accelerateto the first speed and/or the torque at the first speed, when the motoris operating in the second direction. Based on these determinations, thehybrid motor system selects one of the first direction and the seconddirection as the direction in which to operate the motor in the future(e.g., the “normal” direction).

A technical effect of the methods and systems described herein mayinclude one or more of: (a) increasing power factor; (b) reducing EMI;(c) increasing efficiency; (d) enabling variable speed operation of afixed speed PSC motor; and (e) enabling control of the startingacceleration of a fixed speed PSC motor.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed:
 1. A system for controlling a capacity of a compressor,the system comprising: a motor of a compressor including a main windingconnected at a connection point to a start winding; a drive configuredto control a speed of the motor; a first switch configured toselectively couple the main winding to either (a) a first line voltageor (b) a first output of the drive; a second switch configured toselectively connect the connection point to either (a) a second linevoltage or (b) a second output of the drive; a third switch configuredto selectively connect the start winding to either (a) a capacitor or(b) a third output of the drive; and a control module configured tocontrol the drive, the first switch, the second switch, and the thirdswitch by: in response to receiving a demand in a first state: switchingthe first switch to connect the main winding to the first output of thedrive; switching the second switch to connect the connection point tothe second output of the drive; and switching the third switch toconnect the start winding to the third output of the drive; in responseto receiving the demand in a second state: switching the first switch toconnect the main winding to the first line voltage; switching the secondswitch to connect the connection point to the second line voltage; andswitching the third switch to connect the start winding to thecapacitor.
 2. The system of claim 1, wherein the first switch comprisesa group of switches.
 3. The system of claim 1, wherein the first linevoltage is received at a first alternating current (AC) terminal and thesecond line voltage is received at a second alternating current (AC)terminal.
 4. A method for controlling a capacity of a compressor, themethod comprising: in response to a demand indicating a first state:switching, via a control module, a first switch to connect a mainwinding to a first output of a drive; switching, via the control module,a second switch to connect a connection point to a second output of thedrive; and switching, via the control module, a third switch to connecta start winding to a third output of the drive, wherein a motor of acompressor includes the main winding connected at the connection pointto the start winding, wherein the drive is configured to control a speedof the motor; in response to the demand indicating a second state:switching, via the control module, the first switch to connect the mainwinding to a first line voltage; switching, via the control module, thesecond switch to connect the connection point to a second line voltage;and switching, via the control module, the third switch to connect thestart winding to a capacitor.
 5. The method of claim 4, wherein thedrive, the first switch, the second switch, and the third switch areintegrated in a control board.
 6. The method of claim 4 wherein themotor is a fixed-speed motor.
 7. The method of claim 6 wherein the driveenables variable-speed operation of the fixed-speed motor.
 8. The methodof claim 4, wherein at least one of the first switch, the second switch,or the third switch comprises a plurality of switching components. 9.The method of claim 4, wherein the control module is configured toswitch at least one of the first switch, the second switch, or the thirdswitch based on a first threshold or a second threshold.
 10. The methodof claim 9, further comprising: comparing, by the control module, avoltage value applied to the motor with the first threshold, the firstthreshold being a voltage threshold value.
 11. The method of claim 9,further comprising: comparing, by the control module, a current valuemeasured at the motor with the second threshold, the second thresholdbeing a current threshold value.
 12. The method of claim 4, wherein thecontrol module is configured to switch at least one of the first switch,the second switch, or the third switch based on a first range, a secondrange, or a third range.
 13. The method of claim 12, further comprising:comparing a frequency received by operating the motor to a first rangeof line input power frequencies, a second range of line input powerfrequencies, or a third range of line input power frequencies.
 14. Themethod of claim 4, wherein the capacitor includes a first side and asecond side, the first side of the capacitor being connected to thethird switch, and the second side of the capacitor being connected to aline-voltage terminal.
 15. A control system comprising: a firstalternating current (AC) voltage terminal and a second alternatingcurrent (AC) voltage terminal; a motor having a main winding and a startwinding, the main winding and the start winding connected to a commonnode; a motor-drive circuit and a control module configured to control aspeed of the motor; a first switch configured to selectively couple themain winding to the first AC voltage terminal or the motor-drivecircuit; a second switch configured to selectively couple the commonnode of the main winding and the start winding to the second AC voltageterminal or the motor-drive circuit; and a third switch configured toselectively couple the start winding to a capacitor or the motor-drivecircuit.
 16. The control system of claim 15, wherein the first switchcomprises a group of switches.
 17. The control system of claim 15,wherein a first line voltage is received at the first AC voltageterminal and a second line voltage is received at the second AC voltageterminal.
 18. A control system comprising: a line-voltage terminalconfigured to receive an alternating current (AC) voltage; a motorhaving a main winding and a start winding, the main winding and thestart winding connected to a common node; a motor-drive circuit and acontrol module configured to control a speed of the motor; a firstswitch configured to selectively couple the main winding to theline-voltage terminal or the motor-drive circuit; a second switchconfigured to selectively couple the common node of the main winding andthe start winding to the line-voltage terminal or the motor-drivecircuit; and a third switch configured to selectively couple the startwinding to a capacitor or the motor-drive circuit.
 19. The controlsystem of claim 18, wherein the motor-drive circuit, the first switch,the second switch, and the third switch are integrated in a controlboard.
 20. The control system of claim 18, wherein the main windingincludes a first side and a second side and the start winding includes afirst side and a second side, and wherein the common node connects thesecond side of the main winding and the first side of the start winding.21. The control system of claim 18, wherein at least one of the firstswitch, the second switch, or the third switch comprises a plurality ofswitching components.
 22. The control system of claim 18, wherein atleast one of the first switch, the second switch, or the third switch isconfigured to selectively couple based on a first threshold or a secondthreshold.
 23. The control system of claim 22, wherein the controlmodule is configured to: compare a voltage value applied to the motorwith the first threshold, the first threshold being a voltage thresholdvalue.
 24. The control system of claim 22, wherein the control module isconfigured to: compare a current value measured at the motor with thesecond threshold, the second threshold being a current threshold value.25. The control system of claim 18, wherein at least one of the firstswitch, the second switch, or the third switch is configured toselectively couple based on a first range, a second range, or a thirdrange.
 26. The control system of claim 25, wherein the control module isconfigured to compare a frequency received by operating the motor to afirst range of line input power frequencies, a second range of lineinput power frequencies, or a third range of line input powerfrequencies.
 27. The control system of claim 18, wherein the capacitorincludes a first side and a second side, the first side of the capacitorbeing connected to the third switch, and the second side of thecapacitor being connected to the line-voltage terminal.
 28. The controlsystem of claim 18, wherein the motor-drive circuit further comprises: arectifier; an inverter coupled downstream from the rectifier; a directcurrent (DC) link between the rectifier and the inverter; and a DC linkcapacitor coupled across the DC link.
 29. The control system of claim18, wherein the motor is a fixed-speed motor.
 30. The control system ofclaim 29, wherein the motor-drive circuit is configured to enablevariable-speed operation of the fixed-speed motor.